1. Field of the Invention
The invention relates to a shackle which can be attached to the corner of a flexible membrane such as a sail.
2. Description of the Related Art
In many applications, including the field of sailing, it is desired to attach the comer of a flexible membrane, hereafter referred to as a sail, to a line or fixed anchor point. A variety of attachment techniques have been introduced for attaching lines to points of attachment. For instance, U.S. Pat. No. 3,850,468, issued to Hultin on Nov. 26,1974, discloses a chain-like articulation permitting a more direct load between the attaching rope and its point of attachment. Common attachment techniques such as a knot, clip, or other type of existing connecting link, introduce many other undesirable traits to the characteristics of the sail.
U.S. Pat. No. 5,195,223 issued to Tylaska on Mar. 23, 1993, discloses a quick release mechanism which has a required triggering force that remains constant, regardless of the tension being constrained. This invention teaches an equation which yields a logarithmic spiral solution set that provides the configuration necessary to achieve this objective. Tylaska's '223 patent addresses only the problem of quick release and does not consider the specialized problems associated with attaching a sail to a line or anchor point.
Currently, the state of the art is to punch a hole through the corner of the sail and install a grommet, or sew a ring onto the comer of the sail. This ring or grommet is then used to loop through an attachment link such as a standard shackle or D ring. A punched hole or grommet must be located some distance inside from the true projection of the sail corner to provide for enough structural support. Because this grommet is located inward from the corner of the sail, the use of a standard shackle or D ring as an attachment link tends to pull the foot of the sail too far down toward the deck, causing the sail to drag across the surface of the deck unless a different roach cut is performed. The use of a ring tends to hold the foot of the sail too far above the deck, causing wind to seep under. A shackle apparatus that can be used to attach a sail to a line or anchor point that overcomes the shortcomings of using a punched hole, grommet or ring is not disclosed in the prior art.